Final answer:
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it and with a free connection to the ocean. It forms when water from melting glaciers raises the sea level and floods coastal plains and low-lying rivers.
Step-by-step explanation:
An estuary, also known as a drowned river valley, is an estuary that forms when water from melting glaciers raises the sea level and floods coastal plains and low-lying rivers. It is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the ocean. Estuaries are biomes that occur where a source of freshwater, such as a river, meets the ocean. Therefore, both fresh water and salt water are found in the same vicinity, resulting in a diluted (brackish) saltwater.